|HP lists that model as a Micro tower. The power supply will most likely be under capacity and a non standard size.|
I suggest you just start with a new mid to full tower case. Don't buy a case with a power supply. The power supplies that came with cases are usually junk. Buy both separately.
Before you purchase any parts, I suggest you post a list here of what you are considering. You can get feedback from the helpers here that way.
Conversely, If you post what you want the new PC to do and what your budget is, helpers can advise you.